Gas turbine drive drilling apparatus



April 2, 1963 D. s. ROWLEY 3,033,779

GAS TURBINE DRIVE DRILLING APPARATUS Ofiginal Filed Nov. 26, 1957 2 Sheets-Sheet 1 David S. Rowley Inventor April 2, 1963 D. s. ROWLEY' GAS TURBINE DRIVE DRILLING APPARATUS Original Filed Nov. 26, 1957 2 Sheets-Sheet 2 F IG. 5

Inventor A Horney David S. Rowley United States Patent GAS TURBINE DRIVE DRILLING APPARATUS David S. Rowley, Tuisa, Okla, assignor to Jersey Production Research Company, a corporation of Delaware Original application Nov. 26, 1957, Ser- No. 698,978. Di-

vided and this application Feb. 6, 1959, Ser. No-

4 Claims. (Cl. 175-167) This invention concerns the drilling of boreholes, oil wells and the like. It relates especially to the use of gas turbines in the drilling of wells. It relates more specifically to an apparatus and system for drilling boreholes in the earth utilizing a gas turbine unit placed at the bottom of a well bore for driving a drill bit.

This application is a division of my copending application, Serial Number 698,978, filed on the 26th day of November, 1957.

In the art of drilling wells for the production of oil and gas, the most commonly used method is the so-called rotary drilling method. In the rotary drilling method, a drill bit is suspended at the lower end of a string of drill pipe which is supported from the surface of the earth. A drilling fluid is forced down through the drill string, through the drill bit, and back up to the surface through the annulus between the drill pipe and the wall of the borehole. The drilling fluid serves primarily to carry the rock cuttings from the drill bit to the surface. The drill bit obtains its rotary motion from the drill pipe which is rotated at the surface. In the deeper wells, there may be a string of drill pipe several miles long which has to be rotated at the surface in order to rotate the drill bit at the (bottom of the hole. This presents many obvious engineering problems, including a great loss of power in rotating the drill string and a limitation on the amount of rotary power which can be transmitted to the bit at the hole bottom.

The oil drilling industry is quite concerned with the limitations in the ability of the rotary system to deliver suflicient power to the drill bit to maintan a high rate of penetration through the rock. Improved applications of the present method or new and different methods are being sought in order to improve penetration rates. One different method which has recently become of interest is the use of a fluid turbine or mud turbine positioned at the bottom of the Well bore and driven by the drilling fluid. The mud turbine normally includes an external nonrotating or slowly rotating housing, a central shaft supported from the body by various bearing combinations, and a bit at the lower end and driven by the shaft. There are normally rnany turbine stages, usually in the range of 80 to 100, with each stage composed of a stator ring attached to the main body and having blades to direct the fluid toward similar curved blades that are mounted on the shaft, or so-called rotor. The drilling mud in flowing downward through the turbine imparts reaction torques on the blades of the turbine rotor, thus rotating the main shaft which in turn drives the bit. For several reasons, this method has not proven too successful to date. An important problem encountered is that the drilling mud contains abrasives and additives which, when passed through a turbine, cause either eroding or corrosion of the mechanical components thereof, particularly the bearings. A disadvantage of the mud turbine is that its operation requires high fluid pressures at the hole bottom, as in ordinary rotary drilling. These pressures are known to influence adversely the drillability of the rock formation, whereas higher penetration rates are obtained when the fluid pressures at the hole bottom are reduced from ordinary values associated with mud or water drilling.

3,083,779 Patented Apr. 2, 1963 The use of air or gas, replacing the use of drilling mud or water as a cleaning medium in rotary drilling has also been tried recently and with improvement in penetration rates and bit life. Consequently, a drilling system or tool which permits, at the same time, high delivered horsepower at the bit at the hole bottom and takes advantage of penetration rate improvements inherent in drilling with air or gas is highly desirable. This invention provides for an internal combustion bottom-hole gas turbine which accomplishes the objectives of high bottomhole rotary power and permits use of air or gas as the circulating medium. Because the investment in air or gas compressors and compressor prime movers at the surface to supply an equal amount of energy or power to the bottom-hole turbine would be excessive, this invention does not propose the use of a turbine unit for the purpose of extracting power from the expansion of compressed air alone, but it does propose rather that the power delivered be obtained by expansion of hot gases (combustion products) through a gas turbine where the fuel and air required for combustion are both supplied to the unit at the hole bottom through use of multichannel drill pipe and drill collars.

In a preferred embodiment of applicants invention, a "gas turbine is supported at the lower end of a drill collar string which is in turn supported by a drill pipe string which is suspended in a borehole from the surface of the earth. The drill string contains an inner pipe of a reduced diameter from the inside diameter of the drill pipe and drill collars and is utilized for conducting a combustible mixture to the combustion chamber of the turbine at the bottom of the well bore. The annulus between the inner pipe and the drill string is utilized for passing cleaning gas or air through the turbine, where it serves to cool the supporting bearings and the" exterior of the turbine case, and thence out to remove the cuttings of the drill bit, and thence up the annulus between the drill string and the wall of the borehole. Stator elements which include nozzles for directing the flow of combustion gas are supported from the housing of the turbine and are spaced from rotor elements which are carried by a rotatable turbine shaft likewise supported from the housing, and which are positioned in the path of the exhaust from the combustion chamber. The combustible fuel enters the combustion chamber Where it is ignited initially by a pilot flame maintained therein and in usual operation bythe combustion gases themselves through use of flame holders common to ordinary gas turbine combustion chamber design. The hot combustion gases from the cumbustion chamber are then utilized for driving the rotor elements of the shaft. The shaft is thus rotated at a very high speed, and a reduction gear train is used to connect the turbine shaft and the drill bit shaft which is supported from the turbine housing. The turbine housing is attached to the drill collar and remains stationary with respect to the turbine shaft while the turbine shaft rotates at a high speed, thus driving the bit which drills a borehole into the earth. Thrust bearings are provided between the shank of the bit and the" housing of the turbine so that weight may be applied to the bit.

After the hot gases pass through the turbine, they are exhausted into the annulus between the exterior housing of the turbine and the borehole wall. The cleaning fluid is conducted through suitable ports within the main shell containing the turbine and is preferably exhausted through jets or ports in the shank of the drill bit where it picks up formation cuttings and carries them up the annulus to the surface.

One of the objects of this invention is to provide an internal combustion gas turbine operable at the lower end of a string of drill pipe and drill collars in a borehole in "ice aoeawe such a manner as to drive a drill bit while the supporting string is substantially stationary.

Another object is to combine the low bottom-hole hydrostatic fluid pressure advantages of air drilling with the high delivered horsepower of the gas turbine connected to the drill bit.

Other objects will become apparent from the description of the invention taken in reference to the attached drawing in which:

FIGURE 1 illustrates a sectional view of the gas turbine with drill bit attached and positioned in a well bore;

FIGURE 2 illustrates a section view taken at 11-11 of FIGURE 1;

FIGURE 3 is a sectional view taken at III-III in FIGURE 1;

FIGURE 4 is a sectional View taken at IVIV in FIGURE 1; and

FIGURE 5 is a vertical sectional view illustrating the connections between joints of the dual drill string.

Referring to the drawing, in which the best mode contemplated for carrying out the invention is illustrated, and referring in particular to FIGURE 1, a gas turbine is supported from the lower end of a drill collar 12 in the bottom of a borehole 14. The drill collar is attached to the lower end of 'a string of drill pipe. Positioned within drill collar 12 and the drill string is an inner pipe or conduit 16 which is utilized to conduct a combustible mixture from the surface to the combustion charnbersof the gas turbine. An annular space 18 is defined by the outer wall of inner conduit 16 and the inner wall of the drill collar 12 and drill pipe. This annular space 18 conducts a cleaning iluid downwardly. As will be seen, the cleaning fluid passes through the turbine case, but not through the combustion zone, and carries away the cuttings and returns up the annulus 20 between the outer wall of the drill collar 12 and the drill pipe and the wall of the borehole 1d. The cleaning fluid also cools the bearings and other critical parts of the unit.

Supported rat the lower end of drill collar 12 is a turbine case or housing 22 which is preferably attached thereto 'by a threaded joint as shown at 24. Disposed within the turbine case 22 is a combustion chamber 26. Combustible mixture intake manifold 25 connects pipe 116 with the combustion chamber 26. The combustion chamber has a duct downcomer 23 for conducting hot gases to stator elements which are fixed to the walls of hot gas casing 32. Casing 32 is in effect an'enlarged portion of the downcorner 28 and encloses the turbine section. A seal engages turbine shaft 40 at 41 above the turbine section and at 43 below the section. The combustion chamber is supported in the turbine housing by webs 34 and 36, and the downcorner and hot gas casing 352 are supported therefrom by web 38.

Disposed in the center of housing 22 and extending through hot gas casing '32 is turbine shaft 4?. Shaft 40 is supported from the turbine case 22 by webbing 53 and 54 in which the shaft is rotatably mounted. Thrust bearing 42 is provided between shoulder 52, which is attached to or made an integral part of the shaft, and the upper surtface 48 of the webbing 53. Radial bearings 50 are also provided between the webbing 53 and shaft 40. These bearings may be -a roller, journal, or ball bearings as shown, or other suitable types of bearings. The lower end of turbine shaft 40 is supported from the turbine housing 22 by means of webbing 54 which is rigidly attached to or made an integral part of the housing. Radial bearing 56 supports the shaft 4% from webbing 54. Radial bearing 56 near the lower end of the shaft, together with radial bearing 5t and thrust bearing 42 near the top portion of the shaft, permit tunbine shaft 4- to rotate freely while turbine housing 22 is substantially stationary in relation to the rotation of the turbine shaft.

Attached to shmt it) is the rotor element 58 which is positioned from stator element 36. T he hot gas casing 32 encloses the rotor element and stator element and seall ingly engages shaft 45 at 41 above the stator and rotor section and at 43 below the stator and rotor section. A packing medium such as carbon may be used to effect this sealing contact between the shaft and the hot gas casing. The rotor elements and stator elements are positioned in the path of the exhaust of the hot gases from combustion chamber 26, which directs the hot gas downwardly through down-comers 28 and into the chamber defined by the hot gas casing 32. The hot gases impinge upon the curved surfaces of the blades in the stator ring and are directed toward the curved blades of the rotor ring 58. The rotor element is thus rotated at a relatively high speed, turning shaft 4%. Although a multi-stage turbine may be used, adequate horsepower can usually be obtained through use of a single-stage unit, thus conserving costs.

A pilot fiarne nozzle 60 is disposed in combustion chamber 26. Bottles 62 and 64 are held in place in the interior of housing 22 by a metal clamp 65. Bottle 62 is adapted to be filled with a combustible gas under high pressure, and bottle 64 is likewise adapted to be filled with oxygen under high pressure. Regulators 66 and 68 are provided to regulate the amount of fuel and oxygen, respectively, which is passed through line '79 to nozzle 60 to be burned as a pilot within the combustion chamber for igniting combustible gases when they are introduced into the combustion chamber. The combustible mixture is prepared at the surface in facilities not shown by the addition of vaporized rtuel to an oxygen containing gas stream. The resulting combustible mixture is then introduced into the inner conduit 16. The turbine may be started and stopped while it is at the bottom of the hole by respectively starting or stopping the fuel flow into the oxygen containing stream or by stopping the flow of the combustible mixture or the oxygen carrying stream at the surface. When adding or removing a joint of drill pipe, it is de irable to stop the how of :fuel before the oxygen-carrying stream. is stopped. This of course is a safety measure to assure that all the fuel is burned before the connection between the drill string land conduit carrying the combustible mixture is broken.

The hot gases, after passing through the gas turbine, are exhausted to the annulus 29 through ports 72 in the walls of the turbine case 22 and are there diluted with the relatively cooler circulating cooling fluid. Ports 72 are provided with check valves 7 4 which prevent the b ack flow of extraneous materials into the turbine when the turbine is shut down for any reason.

Supported from the lower end of turbine case 22 is a standard tricone drill bit 76 which is provided with ports 86 for the passage of cleaning fluid therethrough. A bit shaft retaining sub is provided at the lower end of turbine case 22 and is connected thereto by threaded joint 11-1. Shank 88 of Ibit 76 is detachably connected to hit drive shaft 112 by threaded joint 89. Retaining ring 119 is connected to sub 116 by threaded joint 118. Thrust bearings 116 are provided between annular shoulders 1:17 of drive shaft E12 and retaining ring 119 at the bottom of case 22. A thrust bearing 12% is also provided between annular houlder 117 and retaining sub 110. In the makeup of the lower portion of this apparatus, shaft 112 is inserted into sub 11%? until shoulders 117 are stopped by thrust bearing 125. Bit shaft retaining sub 11th is then screwed to the main housing 22 at threaded joint 111 The drive shaft 112 is then securely fastened into position. Shank 38 is then joined to hit drive shaft 112.

The gas turbine shaft rotates at a much higher speed than is desirable for the drill bit. Therefore, a reduction gear mechanism 78 is used to connect turbine shaft 44 with the drill bit 76 which reduces the speed of rotation and increases the torque applied to the bit. A suitable reduction gear mechanism 78 is a two-stage planetary gear train including a first gear stage 78 and a second planetary stage 73". A bar 79 is attached to the second planetary stage to rotate drive shaft H2. The gear and bit unit assembly runs in the relatively cool cleaning air or gas medium and can therefore, for example, be prelubrioated on assembly at the surface.

Having described in detail the path of the combustible mixture into the combustion zone and of the combustion products through the turbine section which drives the shaft which in turn through the reduction gears rotates the bit, attention is now directed to the parts of the apparatus defining the path of the cleaning air or gas to the bit and thence to the hole bottom. Cleaning air is passed downwardly through the annular space 18 and enters the turbine case 22 at 80 where it enters into the case interior 82 between the gas combustion chamber and accompanying downcomer and the inner wall of the turbine housing. In other words, the cleaning air passes through essentially all of the interior of turbine housing 22 which is not occupied by the combustion chamber, the combustible fuel inlet conduit, the downcomer, and the hot gas casing which encloses the turbine section. This amounts to a pressurized, continually cooled case. The turbine shaft 46 is hollow, thus defining a conduit 84 which is in communication with the case interior 82 at the upper end and at the lower end in communication with the space between the bit and the borehole below the reduction gear trains. This permits cleaning air to pass therethrough and to cool the shaft. It will be noted that webbings 34, 36, 38, 53 and 54 are arranged such as to provide passageways for the downward flow of cleaning air. The cleaning air, as it passes through the turbine case interior serves to cool the various bearings, the hot gas casing and the gears, thereby permitting operations in a relatively uncontaminated gas medium for improved performance and life of parts. An air passage 86 is providedin bit shank 88 of bit 76 with the upper end of the air passage 86 being in communication with the case interior 82 and the lower end of the air passage 86 being in communication with the exterior of the bit and thereby with the open volume at the hole bottom. Cleaning air passes downwardly through this passage, picks up the cuttings, and carries such cuttings up the annulus 20 to the surface.

Referring now especially to FIGURE 5, an arrangement is illustrated for facilitating the connection or makeup of two separate joints of the dual pipe. The drill pipe and the inner pipe 16 must, as a practical matter, be in sections or joints as in conventional rotary drilling practice and must be progressively fastened together as the drilling proceeds. In the upper joint or section shown in FIGURE the inner pipe will be referred to as 16 and the lower portion as 16"; the upper joint or portion of the drill pipe will be referred to as 13 and the lower portion as 13". An upper part 94 of a tool joint having a box end and a pin end is screwed to matching threads of drill pipe 13' as shown at 92. The upper portion 94 of the tool joint supports inner pipe 16 from drill pipe .13 by webbing 90. Double box end tool joint portion 95 is screwed into matching threads of drill pipe 13 at 97. Inner pipe 16 is supported from the lower tool joint 95 by webbing 8. The dual piping may, of course, be fabricated such that the webbing supports the inner pipe 16 directly from the drill pipe 13. It will be noted that the lower end of inner pipe 16 is protected from damage by not extending below the pin end of upper tool joint portion 94. The upper end 16" of the lower joint of inner pipe is likewise protected by not extending beyond the box end of double box tool joint portion 95. A receptacle 100 for sealing rings 106 is fitted over the lower end of pipe 16 and may be welded thereto as at 102. The lower end of receptacle 100 is of a reduced diameter to fit within inner pipe 16. Strengthening ring '104 may be placed about the upper end of the inner pipe 16". Sealing rings 106 may be O-ring flat seals and are used to maintain the seal between the lower end of receptacle 100 and the inner wall of pipe v16". When it is desired to break the joint of the pipe as illustrated in FIGURE 5, upper tool joint portion 94 is unscrewed from the lower or double box end joint portion 95. As the upper tool joint portion 94 is unscrewed from the lower tool joint portion 95, it is readily seen that sealing rings 106 are withdrawn from interior of the end'of pipe 16" and the upper section of the dual pipe is separated or unjointed from the lower section of dual pipe. Likewise when it is desired to rejoin two sections of dual pipe, the upper box end of tool joint portion is screwed onto matching threads of the pin end of upper tool joint portion 94, and the upper end of inner pipe 16" encloses the reduced end of the receptacle for sealing rings 100, thus effecting a sealing connection between pipe 16 and 16". The effectiveness of this seal is not, however, too critical as the pressure within the inner pipe 16 and within the annular space 18 are maintained normally nearly equal. This equality of pressure is obtained by determining the approximate amount of cleaning fluid needed and the approximate amount of combustible mixture needed and designing the cross-sectional area of the inner pipe in relation to the cross-sectional area of the annular space 18 so that for the desired rate of flow in each passage the pressures of the two fluid streams will be approximately equal.

As the structure of a preferred embodiment of the invention has now been described, attention is now directed briefly to the operations of the invention and some of the advantages associated therewith over conventional rotary drilling and also over the use of the so-called mud turbine. Before assembling the turbine unit with the drill collar, gas cylinder 62 and oxygen cylinder 64 are filled with fuel and oxygen, respectively, under high pressure in order to have sufiicient quantities of oxygen and fuel available for maintaining a pilot flame the desired period of time. Just before the assembled unit is lowered into the borehole, the pilot flame is lighted. When the drill bit is in position for drilling, a combustible mixture is forced downwardly through inner conduit 16 and when reaching the combustion chamber, it is ignited by the pilot. A sufficient velocity is maintained within the inner conduit to prevent flame from the combustion zone from moving upwardly into the inner conduit 16. In other words, the combustible mixture is maintained at a sufficient rate of flow to confine the burning thereof within the combustion chamber. The mixture velocity at the combustion chamber inlet ports exceeds the fiame propagation velocity. Hot combustion gases from the combustion chamber flow downwardly through the duct downcomer 28 and thence through the stator and rotor section whereby the turbine shaft is turned at high speed. The combustion products are then exhausted through check valves 74 into the borehole annulus between the turbine housing and the wall of the borehole. The turbine shaft 40 to which is attached the rotor element is now revolving at high speed. It is of course not desired to rotate the bit at this speed; therefore, reduction gears 78 are used to connect shaft 40 with the drill bit thereby reducing the speed of rotation and also increasing the torque applied to the drill bit. The turbine case and the fixed parts of the drill string may be held stationary or rotated slowly by application of torque at the surface.

At the same time that combustible gas is being forced downwardly through the inner conduit, cleaning fluid such as air or gas, either with or without chemical additives for formation water removal, is being forced downwardly through the annular space 18. The cleaning fluid passes through the interior of the turbine case 22 and thence through ports in the drill bit where it exhausts and picks up cuttings, carrying them back to the surface up through the annular space 20 between the drill string and the wall of the borehole. A portion of the cleaning fluid is passed through the inner conduit 84- of the hollow shaft 40. This aids in cooling the shaft and also in cooling the various bearings and parts in contact with the turbine shaft.

It is obvious that this arrangement permits a wide range 3,oss,779

of torque, speed and horsepower delivered to the rock by use of surface adjustment of the fuel rate and the amount of weight applied through the thrust hearings to the bit while the drilling operations are in progress. When drilling has advanced a distance equal to the length of a joint of pipe, which is normally about 30 feet, the combustible mixture first and then the cleaning gas are shut off thus stopping the rotation of the turbine and also the removal of the cuttings. The fiow of the fuel portion of the combustible mixture is stopped before the oxygen or air portion is. This is to permit all the combustible mixture in the system to be burned before the connection to pipe 16 is broken, thereby removing any potential fire hazard. An additional joint of dual pipe is then connected to the top of the uppermost point of the drill string as is done in conventional rotary drilling practice, and the combustible mixture and cleaning fluid are again connected to the inner pipe and the annular space 18, respectively. As the combustible mixture once more reaches the combustion chamber, it is again ignited by the pilot flame which remains lighted. Gas bottle 62 and oxygen bottle 64 are designed to contain sufficient quantities of fuel and oxygen, respectively, to maintain a small pilot flame at least until the turbine unit assembly has to be removed from the borehole for the purpose of changing bits. When the bit is changed, new cylinders of oxygen and fuel can then be used to replace the at least partially depleted containers.

Some specific advantages will now follow although many advantages of this invention have either been discussed, or are apparent from the above description. As has been seen, the drill string does not necessarily rotate but remains substantially stationary in respect to the rotation of the turbine-driven bit. This of course elimihates the loss of horsepower required for rotating the drill string in the rotary drilling method and would likewise reduce fatigue stresses and premature failures in the drill pipe. The output of the turbine which is located in the bottom of well bore is practically entirely available for rock destruction. The strength of conventional drill pipe permits the use of a wide range of turbine inlet pressures which are used to control the output and overall efiiciency of the turbine including the wide range of torque, speed and horsepower delivered to the rock. This control is obtained simply by surface adjustment of the combustible mixture flow rate and surface control of the weight exerted on the bit by the drill collar string.

Some specific advantages over the mud turbine which may also be advantages over the rotary drilling method include the following. In the operation of mud turbines, the drilling mud is passed through the turbine thus imparting a rotary motion to the shaft of the turbine. The drilling mud contains abrasives which may cause severe wear on the turbine thrust bearings. In the present invention, the cleaning fluid is abrasive-free and all shaft radial and thrust bearings as well as reduction gears operate in a relatively clean environment, thus prolonging the life of these turbine elements relative to the mud turbine. Additionally, gas turbine installations have the lowest ratios of pound of equipment per pound of horsepower output indicating a more compact power unit and much lower first-cost per horsepower output. The location of the drilling of many wells is in arid areas. This makes very expensive the use of mud turbine or conventional mud in rotary drilling which are dependent upon a large water supply but pose no problem to the present invention as it is not dependent upon the use of water as the circulating medium. An additional advantage is that the heat contained in hot exhaust gases from the turbine helps to maintain a dry hole which aids in the removal of formation cuttings.

It is to be understood that various changes and modifications in this invention may be made without departing from the SCOPE reof. For example fuel, without oxygen, may be passed downwardly through inner conduit 16 with air being supplied to the combustion chamber from the cleaning air passageways. Norm-a1 cleaning air would still be supplied to the bit and a portion only diverted for combustion. However, this is not always desirable especially if the cleaning air contains additives which are so affected chemically by burning or heating in the combustion chamber so as to cause a corrosion problem.

I claim:

1. A gas turbine drill assembly having a bit assembly comprising in combination a two-channel drill string, a turbine housing adapted to be supported from the lower end of said drill string, a combustion chamber supported within said housing, means for conducting a combustible mixture through one channel of said drill string to said combustion chamber, hot gas casing adapted to receive hot gases from said combustion chamber, a turbine section supported within said hot gas casing and adapted to be driven by the hot gases with said turbine section being further characterized by having a hollow turbine shaft, means for discharging the turbine section exhaust exterior of said housing, reduction gear means for connecting said turbine shaft to the bit assembly, said bit assembly being characterized by having port means therein, conduit means within said housing establishing fluid communication from the other channel of said drill string through the interior of the hollow turbine shaft to the port means in the bit of said drill.

2. An apparatus as defined in claim 1 with the further improvement of pilot flame means positioned within said combustion chamber.

3. In a gas turbine drill assembly having a bit, the improvement which comprises in combination a two-channel concentric type drill string adapted to be suspended in 'a well bore, a turbine housing adapted to be supported from the lower end of said drill string, a combustion chamber supported within said housing, means for conducting a combustible mixture through the inner channel of said drill string to said combustion chamber, an encased turbine section having a hollow shaft, said turbine section supported within said housing and adapted to receive hot gases from said combustion chamber, bearings supporting said hollow shaft within said housing, exhaust means for discharging the exhaust from said turbine section exterior of said housing, reduction gear means adapted to connect the shaft of said turbine section to the bit, conduit means within said housing adapted for conducting a cleaning fluid therethrough including through said hollow shaft to the lower exterior of said housing so as to cool said shaft and its bearings, and means for conducting a cleaning fluid from the outer channel of said drill string through said conduit means.

4. A gas turbine drill assembly comprising in combination a two-channel concentric type drill string adapted to be suspended in a well'bore, a turbine housing adapted to be supported from the lower end of said drill string; a combustion chamber supported within said housing, a hot gas casing in communication with said chamber and adapted to receive hot gases from said combustion chamber with the cross-sectional area of said casing being less than the cross-sectional area of the interior of said housing; a turbine section within said casing, said turbine section including stator elements rigidly affixed to said casing; a hollow turbine shaft characterized by having the upper'end extending above the upper end of said casing and the lower end extending below the lower end of said casing, rotor elements affixed to said turbine shaft and spaced from said stator elements, radial webbing means rigidly supporting said casing and said combustion chamber from said housing; a second radial webbing means supporting the top portion of said turbine shaft from said housing; radial bearings between said second webbing and said turbine shaft whereby said shaft is rotatable with respect to said housing; a thrust hearing between said second webbing and said shaft whereby thrust from the turbine rotor reaction may be transmitted to said second webbing means; a third webbing means rigidly attached to said housing and supporting the lower end of said shaft from said housing; a second radial bearing supporting the base of said shaft from said third webbing means; connecting means establishing fluid communication between the inner channel of said drill string and said combustion chamber; a conduit adapted to conduct exhaust gases from said turbine section exterior of said housing; a pilot flame means supported within said housing and with the nozzle of said pilot flame means being positioned within said combustion chamber; reducing gear means connecting said shaft with the bit of said drill assembly, said bit being characterized by having ports therein; multiple cleaning fluid passageways within said housing establishing fluid communication between said outer channel and the interior of said hollow turbine shaft and the interior of the housing of said gear means; the interior of said gear housing also being in fluid communication with the interior of the hollow turbine shaft and with ports in the bit of said drill; thrust and radial bearing means supporting the bit assembly from said housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,727,276 Diehl Sept. 3, 1929 1,745,567 Cross et al Feb. 4, 1930 1,790,460 Capeliuschnicofi Jan. 27, 1931 2,371,248 McNamara Mar. 13, 1945 2,663,545 Grable Dec. 22, 1953 2,715,813 Holmes et al Aug. 23, 1955 2,828,945 New Apr. 1, 1958 

1. A GAS TURBINE DRILL ASSEMBLY HAVING ABIT ASSEMBLY COMPRISING IN COMBINATION A TWO-CHANNEL DRILL STRING, A TURBINE HOUSING ADAPTED TO BE SUPPORTED FROM THE LOWER END OF SAID DRILL STRING, A COMBUSTION CHAMBER SUPPORTED WITHIN SAID HOUSING, MEANS FOR CONDUCTING A COMBUSTIBLE MIXTURE THROUGH ONE CHANNEL OF SAID DRILL STRING TO SAID COMBUSTION CHAMBER, HOT GAS CASING ADAPTED TO RECEIVE HOT GASES FROM SAID COMBUSTION CHAMBER, A TURBINE SECTION SUPPORTED WITHIN SAID HOT GAS CASING AND ADAPTED TO BE DRIVEN BY THE HOT GASES WITH SAID TURBINE SECTION BEING FURTHER CHARACTERIZED BY HAVING A HOLLOW TURBINE SHAFT, MEANS FOR DISCHARGING THE TURBINE SECTION EXHAUST EXTERIOR OF SAID HOUSING, REDUCTION GEAR MEANS FOR CONNECTING SAID TURBINE SHAFT TO THE BIT ASSEMBLY, SAID BIT ASSEMBLY BEING CHARACTERIZED BY HAVING PORT MEANS THEREIN, CONDUIT MEANS WITHIN SAID HOUSING ESTABLISHING FLUID COMMUNICA- 